[FEAT] terms table: basic cache for the search and pagination filters (now they're restored after page reload)

- List cleaned
- Dynamic graph saved each time
- Removing page authors (for later)

[FEAT] Adding new page for authors. TODO: split auhors list. @rloth: can you easily do that with facets ?

[FEAT] Adding robots.txt rules (/api/ should not be known and we do not divulgate this informations to malwares); check the logs to improve it.

[FIX] prevent nodes_ngrams_count.items() KeyError by forcing nodes_ngrams_count to use same key as ngrams_data when key is truncated

- mail notification improved
- import url from settings
- message upated (links to gogs removed in the message, still present in
  the interface)

- Graphs are in an ordered list
- Informations with start/end and number of nodes
- User can choose to compute with conditional or distributional distance